This is a study of bile acid metabolism and the alterations associated with intestinal disease, diet and certain drugs. The changes in the enterohepatic circulation of cholic and chenodeoxycholic acid will be studied under various circumstances. The simultaneous fecal excretion of labelled bile acid and of a non-absorbable marker (Cr51Cl3) will be measured. Not only can excretion rates of the bile acids be determined, but a coefficient of absorption for each bile acid can be calculated. Emphasis will also be placed on a detailed examination of physical state of bile acids in the intestinal lumen. This will include an evaluation of bile acid detergent capacity and the extent of lipid absorption in relation to changes in physical state of bile acids. The important factors that influence the physical state such as drugs, dietary adsorbants and especially microflora will be examined. The basic technique employed will be intubation of the proximal small intestine and the frequent aspiration of intestinal contents during and after meals for 24 hours. The interrelations between bile acids and intestinal microorganisms will be explored further by studying the microflora of the ileum and cecum, and modification induced by increasing and decreasing the intestinal bile salt concentrations.